WASHINGTON - The former U.S. ambassador to the United Nations said Iran should be attacked before it builds a nuclear bomb, a newspaper reported Wednesday.

"If the choice is between a nuclear-capable Iran and the use of force, then I think we need to look at the use of force," John Bolton told The Daily Telegraph of London.

Bolton said the use of force should be a last resort but that diplomatic efforts to convince Iran to abandon its nuclear program had failed.

"It's been conclusively proven Iran is not going to be talked out of its nuclear program. So to stop them from doing it, we have to massively increase the pressure," he said.

Bolton's interview appeared as reports surfaced that Iran had made more progress than observers realized in enriching uranium, the Telegraph reported.

Experts had estimated that Tehran was four years away from producing enough uranium to build one nuclear bomb but a leaked report from the U.N. International Atomic Energy Agency about Iran's Natanz nuclear installation found that scientists there had made more progress than previously thought, the newspaper reported.